Fonzie and Richie talk about possibly being in a movie together. 5 years later, the actors playing them were in the movie Night Shift, with Henry Winkler starring and Ron Howard directing and having cameos in multiple scenes.
The Jump the Shark thing has more layers than just Fonzie jumping a shark and a website, and then a common saying, being named after it, thus summarizing when shows go bad, because this is the first episode that "threatens" the fact that Ron Howard's Richie may be leaving, as in, to become an actor in Hollywood. Most fans agree that the true Jump the Shark moment, that is, when the show got so bad there was simply no turning back, was when Richie left (Ralph too). Ironically, when Richie left for the army, he later returned for a guest spot, and his dream was again for a Hollywood career, but as a screenwriter. (It's also ironic that Ron Howard would become a huge director after the series.)